1. Field of the Invention
The present invention relates to paper-making machines, and, more particularly, to a wet end of a paper-making machine.
2. Description of the Related Art
A wet end of a paper-making machine partially includes a headbox, a wire and a former associated with the wire. The headbox receives prepared fiber stock in the form of a prepared fiber suspension. The headbox has a nozzle section which extends substantially across the width of the wire and the fiber stock is discharged with a known cross sectional profile from the nozzle section onto the wire.
It is known to provide a turbulence generator at the inlet to the headbox. The turbulence generator assists in deflocculating the fiber stock which enters the headbox. For example, referring to FIG. 1, it is known to provide a turbulence generator in the form of a diffuser plate which is attached to the inlet of the headbox. The diffuser plate includes a plurality of through holes which are disposed substantially parallel to each other and extend in the flow direction toward the inlet of the headbox. The diffuser plate provides a more even flow distribution of the fiber stock which is transported into the headbox and assists in deflocculating the fiber stock. The diffuser plate may be connected in a conventional manner with a tapered header. The taper angle on the tapered header is selected such that the velocity decrease caused by fiber stock flowing through the through holes in the diffuser is substantially offset by the velocity increase caused by the reduced cross sectional area associated with the taper angle, thereby resulting in a substantially constant flow rate into the headbox across the diffuser plate.
It is also known to provide a turbulence generator in the form of a tube bundle including a plurality of tubes which are connected at one end thereof to the headbox inlet, and connected at the other end thereof to a source of fiber stock. A tube bundle of this type also assists in deflocculating the fiber stock entering the headbox inlet. Such a tube bundle is incorporated into the "VALLEY" headbox marketed by the assignee of the present invention.
It is further known to control "on the fly" the concentration of the fiber stock which is transported into a headbox. Varying the concentration of the fiber stock immediately prior to the fiber stock entering the headbox inlet is known as "dilution control". For example, with a headbox including a diffuser plate with a plurality of through holes as described above, it is known to inject clean water into the fiber stock flowing through a particular through hole to thereby dilute the fiber stock to a particular concentration. A problem with using clean water for dilution control in this manner is that the clean water is obtained from a source, such as well water, having a temperature and Ph which are different from the fiber stock flowing through the associated through hole in the diffuser plate. Thus, heat and/or chemicals may need to be added to the clean water to obtain the proper temperature and Ph. A more significant problem is that the introduction of clean water into the flow of fiber stock which is flowing through a through hole in the diffuser plate causes a local increase in the flow rate of the fiber stock which flows through the headbox. This local flow rate generally is transmitted to the nozzle, resulting in a localized increased flow rate of the fiber stock from the nozzle which is undesirable.
It is also known to provide dilution control in conjunction with a conventional hydraulic headbox. For example, it is known to provide a relatively large tapered header through which headbox consistency fiber stock flows. The headbox consistency fiber stock is transported from the larger tapered header through a plurality of fluid passages. A smaller tapered header carries lean whitewater which is recirculated from the portion of the wet end associated with the wire and former(s). The lean whitewater is primarily water which has drained from the fiber stock carried on the wire in the wet end, but also includes a small amount of fibers therein. The lean whitewater is substantially at the correct temperature and Ph since it has already been treated prior to being previously introduced into the headbox. The lean whitewater is transported from the smaller tapered header through a plurality of fluid passages which respectively merge with the fluid passages associated with the larger tapered header. Depending upon the angle between each pair of merging fluid passages and the flow rate of the lean whitewater through the fluid passages, the main flow through the fluid passages associated with the larger tapered header may be somewhat retarded to provide dilution control without increasing the flow rate from each fluid passage. Such a dilution control apparatus thus provide effective dilution control without changing the localized flow rate of the fiber stock flowing through the headbox. A dilution control apparatus of this type is marketed by the assignee of the present invention under the trademark "MODULE JET".
Heretofore, the MODULE JET dilution control apparatus as described above has not been used in conjunction with a headbox with a turbulence generator as described above. More particular, the fluid passages associated with the module jet dilution control apparatus define an outlet with a row of essentially aligned outlet holes extending across the width of the module jet. The cross sectional area of the outlet for the module jet is thus relatively small. On the other hand, the various through holes or tubes in a diffuser or tube bundle, respectively, include inlets which are spaced relatively far apart in order to prevent "stapling" or buildup of the fibers on the lands between the through holes or tubes. Thus, the inlet area to a turbulence generator in the form of a diffuser or a tube bundle is substantially larger than the outlet of the module jet dilution control apparatus.
The module jet dilution control apparatus as described above also allows for "fiber orientation" of the fiber stock which is discharged from the nozzle of the headbox onto the wire of the wet end. In general, fiber orientation is the direction which each fiber generally extends relative to the running direction of the machine when the fiber stock is discharged onto the wire. It has been found to be preferable to orient the fibers of the fiber stock on the wire at a relatively small acute angle relative to the machine running direction. The module jet fiber orientation apparatus has been found to be effective in providing fiber orientation of the fiber stock on a wire as well as dilution control.
What is needed in the art is a device which allows a fiber stock delivery device providing both dilution control and fiber orientation to be used in conjunction with a headbox having a turbulence generator, without adversely affecting the flow characteristics of the fiber stock which is discharged from the headbox onto the wire of the paper-making machine.